The mettle of the man who aspires to be a future Liberal leader is about to be severely tested, now that Malcolm Turnbull has handed Peter Dutton his dream home affairs ministry, overseeing a vast national security empire.

Dutton comes to the job with, at best, a middling ministerial record. His time in the health portfolio was a nightmare. In immigration he has been relentlessly political.

The former Queensland policeman is a natural political head kicker rather than a nuanced policy man.

It was Malcolm Turnbull who, among other ministers, tore shreds off a 2015 Dutton submission on removing citizenship from people involved with terrorism.

A recent initiative, revamping foreign worker visas, has brought problems for and complaints from business. The announced toughening of the citizenship requirements that makes the English test excessively difficult has been sharply criticised.

Dutton has not so far managed to secure the departure of any of the refugees from Manus Island and Nauru that the United States agreed to take.

When he became leader Turnbull wouldn’t have Dutton on cabinet’s national security committee. He fought his way back into that key group. He and Turnbull drew close. With Liberal conservatives coalescing around him as their factional heavyweight, Dutton made himself a guardsman for the Prime Minister.

Turnbull is understandably sensitive to suggestions that the planned home affairs ministry is all about Dutton, whose continued support is so vital to him.

Those around the Prime Minister insist Turnbull has long been committed to a shake up of national security arrangements, exploring the issues on overseas trips.

But you have to ask: if there were no Dutton would Turnbull be putting the government through what he is presenting as the biggest reorganisation in four decades, which is going to take many months and a vast amount of effort to implement? Wouldn’t it be a matter of fine tuning rather than root and branch change? After all, the evidence - and the mantra from the government - is that things are working well.

Whatever the motives, and regardless of their personal thoughts, ministers have to defend the new arrangements. This led Attorney-General George Brandis - a long-time opponent of the shift that will cost him responsibility for ASIO – into an unexpected and unconvincing argument at Tuesday’s press conference, which brought together with Turnbull the winner and losers (Dutton, Brandis and Justice Minister Michael Keenan, who cedes the Australian Federal Police).

Not only did Brandis speak enthusiastically about the new arrangements, but he pointed out that because of his multiple responsibilities he hadn’t been able to focus exclusively on his national security duties.

It sounded like the barrister making a case. If one had put to Brandis six months ago that the present arrangement was unsatisfactory, it’s a fair bet he’d have been dismissive.

But Brandis has retained his responsibility for issuing warrants under the ASIO Act, a power the attorney-general will share with Dutton. They will both have to approve warrants, except in cases where time is of the essence.

One-time ASIO head Dennis Richardson said on Tuesday: “It’s a good thing the attorney-general remains the approval authority for ASIO warrants.” But “it does mean ASIO is effectively responsible to two ministers not one”.

Richardson, in contrast to the government and many commentators, plays down the significance of the broad reorganisation, seeing much of it as presentational.

If Brandis had trouble with multi duties, Dutton is likely to have the problem in spades, given the breadth of his responsibilities, that will range from border security to oversight of ASIO, the AFP, Australian Criminal Intelligence Commission, and much else. The bundle labelled “national security” has varied components.

Most security experts have either challenged the need for change, or said that what is planned is undesirable. Neither Turnbull nor Dutton will be drawn on whether the heads of ASIO or the AFP advocated that they move ministers – because, on all we know, they didn’t.

Turnbull is aware of the dangers of excessively concentrated power – hence his effort to beef up the attorney-general’s scrutiny remit. The first law officer was “the minister for oversight and integrity and that role is being reinforced”, he said. How vigorously this responsibility will be exercised will depend on who occupies the portfolio - Brandis is expected to leave parliament in a few months.

While co-ordination is vital, one risk that has been raised is that too much centralisation can push out counter opinions. It will be up to Turnbull to stop that from happening.

The planned new Office of National Intelligence (ONI), which will subsume the present Office of National Assessments, will report directly to the Prime Minister.

The office was proposed by the L'Estrange/Merchant Independent Intelligence Review, in a report released on Tuesday. That review, incidentally, did not recommend a Home Affairs portfolio - although those in the prime ministerial circle stress that it did not recommend against one.

The review says the office “would be headed by a Director-General who would be the Prime Minister’s principal adviser on matters relating to the national intelligence community.”

Who gets this job and how much Turnbull listens to them will be absolutely critical in how the new centralised system under a highly assertive minister operates. Turnbull and the director of the ONI potentially could be the counterweight to Dutton and the Home Affairs department.